This invention relates to a bridge deck system and, more particularly, to a system for attaching a prefabricated bridge deck panel to a bridge structure.
A bridge deck is that portion of the bridge which supports and transfers traffic loads to the primary structure of the bridge. It may be a steel-reinforced, poured-in-place concrete structure or may be made up of prefabricated assemblies. Bunker U.S. Pat. No. 1,929,478, for example, describes a prefabricated floor slab having a steel pan which contains a steel-reinforcing bar or mesh welded to the pan and filled with concrete or other filling material. The pan may be attached to flanges of underlying beams with bolts, by welding, or with clamps which are bolted to the pan and underlie the beam flange. Orthotropic designs are also particularly suitable for making bridge deck structures. The November 1967 issue of Civil Engineering--ASCE magazine includes an article entitled "Aluminum Orthotropic Bridge Deck" which describes a bridge deck panel system which was used in 1967 on the Smithfield Street bridge in Pittsburgh, Pa. to replace the existing bridge deck. At least one reason an aluminum orthotropic design was used was to minimize the dead weight as much as possible. The bridge was 85 years old at the time, and in order to raise the load limit to suitable levels of 1967 traffic, it was necessary to minimize the dead load of the new deck. The aluminum deck was fabricated from aluminum plate welded to ribbed extrusions. The extrusions are substantially U-shaped in cross section with the legs of the U sloping slightly upwardly and outwardly from the base. Flanges extending outwardly from the base on each side are provided to attach the deck to the underlying bridge structure. Thus, the extrusions are frustoconical in cross section with the distance between the legs or ribs progressively increasing from their connection at the base to their free ends. The extrusions are assembled with the plate by welding the free ends of the ribs thereto. They are welded to the plate parallel with one another along the length of the plate and spaced uniformly apart, centerline to centerline, a distance of 161/8 inches. Spacing of the extrusions is an element of design of the deck to carry the anticipated traffic loads. The traffic side of the plate was coated with a sand impregnated polyester as a traction and wear surface. The panels were fabricated as large as possible consistent with the bridge dimensions since the weight of the complete deck was only 15 pounds per square foot. Thus, the panels were typically 10'9" wide by 27'73/8" long, weighing approximately 4500 pounds, and were easily maneuvered and set in place on the bridge floor beams with a minimal amount of labor. To attach the deck to the bridge structure, the flanges on the ribbed extrusions were firmly bolted to floor beam flanges. Transverse joints between adjacent panels were filled with a 1/4 inch bituminous filler board, and the longitudinal joint between panels was sealed with an acrylic terpolymer sealant to allow for expansion and contraction of the panels. Since the floor beams on the Smithfield Street bridge are also aluminum having substantially the same coefficient of expansion as the bridge deck, no provision was made in the connection between the deck and floor beam to accommodate a difference in movement between the deck and floor beams due to temperature change.
In 1983 the Federal Highway Administration reported to Congress that 45% of the 565,000 bridges in place in the United States were in need of repair. Of those bridges, it was estimated that as many as 65,000 have structural deficiencies which could be remedied by replacing the existing heavy deck systems with a lighter deck. It is not believed that these figures have substantially changed since that 1983 report. A large percentage of those bridges are steel fabricated having a steel floor beam system supporting the bridge deck. Because of its light weight and quick installation with minimal equipment and labor, an aluminum orthotropic bridge deck is particularly well suited for use in replacing deteriorated bridge decks. Since the coefficient of expansion of aluminum is approximately twice that of steel, an aluminum deck will be substantially more responsive to temperature changes than the underlying bridge structure. If the deck is restrained from movement at its connection with the bridge, the deck or connection may be stressed to unacceptably high levels and/or accelerate a fatigue failure from imposition of higher forces during stress reversal cycles. It is desirable, therefore, to provide a system for attaching a bridge deck to a bridge structure which will enable the deck to be securely anchored and yet free to move independently of the structure in response to changes in temperature.